The secondary transfer unit has a contact separation mechanism that contacts the secondary transfer roller to the image carrier when a toner image formed on the image carrier is transferred to a sheet but separates the secondary transfer roller from the image carrier when the toner image formed on the image carrier is not transferred to the sheet.
In a secondary transfer unit having a mechanism for contacting and separating the secondary transfer roller to and from the image carrier, drive apparatuses for contacting and separating the secondary transfer roller have been known that the number of parts of a mechanism section constituting the mechanism for contact and separation operation does not increase and a device such as an electromagnetic clutch requiring electrical control is not used. Such a drive apparatus is disclosed in JP-A-2007-264546.
On the other hand, image forming apparatuses equipped with a mechanism for scrapping off toner remaining on the secondary transfer roller to clean by contacting a cleaning blade to the secondary transfer roller. Moreover, in order to increase a lifetime of the secondary transfer roller and prevent winding of the cleaning blade, a mechanism has been known that coats lubricant on a surface of the secondary transfer roller by using a fur brush. As lubricant, solid zinc stearate is used. The zinc stearate is provided in a holding member, and is pressed by a spring toward a fur brush.
The holding member is formed of a high stiffness member such as a metal plate, and is integrally formed with a zinc stearate.
The zinc stearate is a brittle member which is stiff and frail. Hence, when the zinc stearate is integrally formed with a holding member made of a metal plate and the zinc stearate is attached in a state where the metal plate is greatly bent, a problem that the zinc stearate is cracked is encountered. Therefore, a size of the metal plate should be precisely controlled, and so work becomes complicated.
Furthermore, in order not to buckle and deform a spring for pressing the zinc stearate against the fur brush, it is necessary to caulk a stud in the holding member. Thus, the number of parts increases.
On the other hand, a seal member (side seal) is attached to a secondary transfer roller housing section at each position of both sides of the secondary transfer roller. The secondary transfer roller and the seal member are disposed to be engaged with each other. Thus, toner leakage from the side of the secondary transfer roller is prevented. Furthermore, a gap between the cleaning blade and the side seal is formed as small as possible in consideration of the toner leakage.
The cleaning blade is supported by the blade supporting plate. In this case, gap is generated between the blade supporting plate and the secondary transfer roller housing section by accumulation of tolerance. The blade supporting plate is movable in an axial direction of a supporting shaft in accordance with the gap width.
Since the cleaning blade is movable in front and back directions, the cleaning blade may be overlapped with the side seal. A part of the cleaning blade overlapped with the side seal is lifted by a thickness of the side seal, and thus unevenly comes into contact with the secondary transfer roller at the lifted position. Hence, cleaning error and blade winding are caused. In addition, since a gap is generated between the side seal and the blade end portion on a side opposite to a side overlapping with the side seal, there is concern about toner leakage because of the gap.
Generally, to eliminate gaps, the blade supporting plate is equipped with a plate spring, the plate spring comes into contact with the secondary transfer roller housing section, and thereby the blade supporting plate is disposed close to any one part of the front and the back of the secondary transfer roller housing section. With such a configuration, rattle due to the gap is eliminated. However, since mountability is not so good and a number of flexures are caused, lifetime thereof is short and the total volume of materials is large, and thus cost increases.